Conventional injection blow molding apparatus operates through a cycle beginning with the injection of plastic material into an injection mold containing a core rod. A parison is formed around the core rod, and the injection mold then opens and permits the core rod to move to the next performance station.
The second station is usually a blowing mold in which the parison is blown to the desired shape of a finished article; and when the blown article cools sufficiently, it is removed from the blowing mold and transferred to a stripper station. At the stripper station the blown article is removed from the core rod.
One of the limitations on the speed of a conventional cycle is the time required to cool the blown article sufficiently to remove if from the blowing mold and to the stripper station. One of the principal purposes of this invention is to cool the blown article more quickly and thereby reduce time cycle of the machine and correspondingly increase the production of the blow molding machine.
This invention includes, in its preferred embodiment, an elastic balloon which is attached to a core rod assembly in position to hug the core rod when the balloon is deflated. When a parison is formed over the core rod, it is applied over the outside of the collapsed balloon and over a short length of the core rod assembly beyond the end of the balloon. This short length of the parison is the portion which forms the mouth or neck of the article to be blown and it is a portion of the parison which is not expanded in the blow mold.
The balloon has two important advantages. One is that it permits the blown article to be cooled from the inside. Cooling fluid can be circulated through the inside of the balloon during a blowing operation and immediately after the completion of the blowing operation. The core rod of this invention is constructed so that cooling fluid flows from inside the core rod into the space between the core rod and the expanding balloon and parison; and this cooling fluid exhausts through other passages communicating with exhaust openings in the side of the core rod. If desired, fluid of any temperature can be circulated for the purpose of obtaining an orientation temperature of the parison before its final expansion to the shape of the desired article.
Part of the construction of this invention relates to the way in which the balloon is attached to the core rod assembly in such a way that the balloon connection to the core rod assembly is not subjected to any axial pull when the blown article is being stripped from the core rod. In the preferred construction, a sleeve which has a shoulder on one end, serves as part of the parison supporting surface of the core rod assembly. The balloon is attached to the core rod assembly in an undercut cavity at the shoulder of the sleeve and the diameter of the collapsed balloon is less than that of the sleeve so that the balloon is protected from axial pull when an article blown on the core rod assembly is stripped from the core rod assembly by a stripper plate bearing against the part of the blown article that is formed on the surface of the sleeve.
The invention also includes several provisions for admitting air between the blow parison and the outside surface of the balloon so that the balloon can collapse after the parison is fully blown to the shape of the desired article. Without provision for admitting air between the outside surface of the balloon and the blown parison, the balloon would be prevented from collapsing, independently of the blown parison, because of the existence of vacuum between the parison and the balloon.
One modification of the invention has provision for circulating fluid within the parison to control the temperature and more specifically to reduce the temperature quickly. This modification also has provision for cooling the parison from the outside by circulating cooling fluid into contact with the outside of the parison in the blowing mold. A special type of blowing mold can be used in which the article is blown within a shroud having a multitude of openings into which fluid enters to form a fluid cushion, preferably an air cushion, inside the shroud. The article is blow into contact with this cushion which increases in pressure as the parison expands toward the inside surface of the shroud. This blowing of the parison against an air cushion instead of into contact with a solid surface is intended especially for use with containers having rigid mouth or neck portions and flexible and pliant body portions.
Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.